In diverse service scenarios of the fifth generation mobile communications technology (5G), different orthogonal frequency division multiplexing (OFDM) waveform parameters are required for the service scenarios. However, it is an inevitable requirement on a 5G basic waveform that an OFDM waveform parameter can be dynamically selected and configured based on a service scenario while advantages of conventional OFDM are also considered.
Filtered-OFDM (f-OFDM for short) based on an OFDM subband is a waveform technology that can meet a 5G requirement. In the f-OFDM waveform technology, a system bandwidth is divided into a plurality of OFDM subband frequency-domain signals. Each OFDM subband has features of a conventional OFDM waveform, and a high-order digital shaping filter is used to perform OFDM subband filtering on each OFDM subband. Because the high-order digital shaping filter is used to perform OFDM subband filtering in a time domain, each filtered OFDM subband has favorable out-of-band performance in a frequency domain, so that decoupling of each OFDM subband waveform is implemented. Further, a different waveform parameter can be configured for each OFDM subband based on an actual service scenario while advantages of the conventional OFDM waveform are combined. For example, FIG. 1 is a schematic diagram of processing an OFDM subband frequency-domain signal in the prior art. A bandwidth of the OFDM subband frequency-domain signal is 20 MHz. As shown in FIG. 1, a 2048-point inverse fast Fourier transform (IFFT) is first performed on the OFDM subband frequency-domain signal to obtain a time-domain signal. A cyclic prefix is added to each time-domain signal, and a high-order digital shaping filter filters each signal to which the cyclic prefix has been added. All filtered signals are combined and transmitted by means of radio frequency (RF).
The high-order digital shaping filter is used in the f-OFDM waveform technology, to make a filtered signal have favorable out-of-band performance (for example, a very narrow transition band), overheads of guard space required between adjacent OFDM subbands may be very low, and even no guard space is required in most scenarios. However, because OFDM subband signals in f-OFDM are all broadband signals (for example, it is specified in Long Term Evolution (LTE) that a bandwidth of an OFDM signal is 20 MHz), and a signal sampling rate is high, if such high-order time domain filtering is performed at a relatively high sampling rate, implementation complexity is very high, and for an entire system, the following problems are caused: (1) For a terminal, filtering with high complexity is adverse to energy saving of the terminal, and in particular, for numerous low-cost terminals that may exist in the system, implementation of the high-order digital shaping filter is a relatively big bottleneck. (2) A high-order digital filter needs to take a relatively long processing time on either a transmitter side or a receiver side, and this is especially adverse to a typical ultra-low delay service requirement in 5G. Therefore, to design a digital shaping filtering scheme with low complexity becomes a core issue of the f-OFDM technology.